Yemen, ravaged by war, hunger and disease, is seeing a spike in diphtheria cases that will inevitably erupt into a larger, deadly outbreak because so few people have been immunised, according to aid officials.

At highest risk are children, who account for many of the more than 280 suspected diphtheria cases and 33 associated deaths reported as of Tuesday, according to the World Health Organisation.

Most of the cases and deaths involved children who had not been immunised against the disease, a contagious and potentially fatal bacterial infection that spreads easily, the WHO said.

The diphtheria spread is inevitable in Yemen due to low vaccination rates, lack of access to medical care and so many people moving around and coming in contact with those infected, said WHO and officials with Médecins Sans Frontières.

Yemen’s civil war has killed more than 10,000 people and displaced more than two million others.

Diphtheria spreads as easily as the common cold through sneezing, coughing or even talking, according to health officials, but it is easily preventable by vaccination.

Yemen is also battling a cholera epidemic that has infected about one million people and caused more than 2,000 deaths.

Diphtheria could be more fatal than cholera, especially among unvaccinated children under five years old, according to MSF, which says as many as two-in-five diphtheria cases end in death.

Yemen is also facing soaring food prices and fuel shortages, and some 8.4 million Yemenis are considered to be a step away from famine, the United Nations has said.

A Saudi-led military coalition fighting the Iran-aligned Houthi movement in Yemen's civil war blockaded ports last month.

The blockade has eased, but its impact limited supplies of desperately needed fuel, food and medicine, aid officials say.

"Even for patients who want to seek treatment, the blockade on fuel and consequent surge in prices means that they cannot afford to travel to the very few health centres still operational," MSF said.